Bottom Line:
However, abacavir had no effect on ecto-5' nucleotidase and nucleoside transporters.Short-term and long-term treatment of abacavir did not affect acetylcholine-induced relaxation in rat basilar arteries.It is speculated that abacavir-induced cardiovascular risk may not be related to endothelial dysfunction as abacavir does not impair relaxation of blood vessels.

Affiliation: Department of Pharmacology and Pharmacy, Faculty of Medicine, The University of Hong Kong, Hong Kong, China.

ABSTRACT

Background: The use of abacavir has been linked with increased cardiovascular risk in patients with human immunodeficiency virus infection; however, the mechanism involved remains unclear. We hypothesize that abacavir may impair endothelial function. In addition, based on the structural similarity between abacavir and adenosine, we propose that abacavir may affect vascular contractility through endogenous adenosine release or adenosine receptors in blood vessels.

Methods: The relaxation effect of abacavir on rat basilar arteries was studied using the myograph technique. Cyclic GMP and AMP levels were measured by immunoassay. The effects of abacavir on nucleoside transporters were studied using radiolabeled nucleoside uptake experiments. Ecto-5' nucleotidase activity was determined by measuring the generation of inorganic phosphate using adenosine monophosphate as the substrate.

Results: Abacavir induced the relaxation of rat basilar arteries in a concentration-dependent manner. This relaxation was abolished when endothelium was removed. In addition, the relaxation was diminished by the nitric oxide synthase inhibitor, L-NAME, the guanylyl cyclase inhibitor, ODQ, and the protein kinase G inhibitor, KT5820. Abacavir also increased the cGMP level in rat basilar arteries. Abacavir-induced relaxation was also abolished by adenosine A2 receptor blockers. However, abacavir had no effect on ecto-5' nucleotidase and nucleoside transporters. Short-term and long-term treatment of abacavir did not affect acetylcholine-induced relaxation in rat basilar arteries.

Conclusion: Abacavir induces acute endothelium-dependent relaxation of rat basilar arteries, probably through the activation of adenosine A2 receptors in endothelial cells, which subsequently leads to the release of nitric oxide, resulting in activation of the cyclic guanosine monophosphate/protein kinase G-dependent pathway in vascular smooth muscle cells. It is speculated that abacavir-induced cardiovascular risk may not be related to endothelial dysfunction as abacavir does not impair relaxation of blood vessels. The most likely explanation of increased cardiovascular risk may be increased platelet aggregation as suggested by other studies.

pone.0123043.g006: Effect of abacavir on the concentration of cAMP in rat basilar arteries.Rat basilar arteries were incubated without (control) or with 30 μM abacavir for 20 min. cAMP content in arteries was determined using an ELISA kit. Values are means ± S.E.M. of three sets of experiments and statistical comparisons were made using student’s t-test.

Mentions:
To further confirm that abacavir-induced relaxation was mediated by the cGMP signaling pathway, but not by the cAMP signaling pathway, the effects of abacavir on the levels of cGMP and cAMP in rat basilar arteries were investigated. The intracellular concentration of cGMP in rat basilar arteries was increased by abacavir (30 μM) (Fig 5). The increased level of cGMP by abacavir was diminished by ODQ (10 μM). In contrast, abacavir had no effect on cAMP level in rat basilar arteries (Fig 6).

pone.0123043.g006: Effect of abacavir on the concentration of cAMP in rat basilar arteries.Rat basilar arteries were incubated without (control) or with 30 μM abacavir for 20 min. cAMP content in arteries was determined using an ELISA kit. Values are means ± S.E.M. of three sets of experiments and statistical comparisons were made using student’s t-test.

Mentions:
To further confirm that abacavir-induced relaxation was mediated by the cGMP signaling pathway, but not by the cAMP signaling pathway, the effects of abacavir on the levels of cGMP and cAMP in rat basilar arteries were investigated. The intracellular concentration of cGMP in rat basilar arteries was increased by abacavir (30 μM) (Fig 5). The increased level of cGMP by abacavir was diminished by ODQ (10 μM). In contrast, abacavir had no effect on cAMP level in rat basilar arteries (Fig 6).

Bottom Line:
However, abacavir had no effect on ecto-5' nucleotidase and nucleoside transporters.Short-term and long-term treatment of abacavir did not affect acetylcholine-induced relaxation in rat basilar arteries.It is speculated that abacavir-induced cardiovascular risk may not be related to endothelial dysfunction as abacavir does not impair relaxation of blood vessels.

Affiliation:
Department of Pharmacology and Pharmacy, Faculty of Medicine, The University of Hong Kong, Hong Kong, China.

ABSTRACT

Background: The use of abacavir has been linked with increased cardiovascular risk in patients with human immunodeficiency virus infection; however, the mechanism involved remains unclear. We hypothesize that abacavir may impair endothelial function. In addition, based on the structural similarity between abacavir and adenosine, we propose that abacavir may affect vascular contractility through endogenous adenosine release or adenosine receptors in blood vessels.

Methods: The relaxation effect of abacavir on rat basilar arteries was studied using the myograph technique. Cyclic GMP and AMP levels were measured by immunoassay. The effects of abacavir on nucleoside transporters were studied using radiolabeled nucleoside uptake experiments. Ecto-5' nucleotidase activity was determined by measuring the generation of inorganic phosphate using adenosine monophosphate as the substrate.

Results: Abacavir induced the relaxation of rat basilar arteries in a concentration-dependent manner. This relaxation was abolished when endothelium was removed. In addition, the relaxation was diminished by the nitric oxide synthase inhibitor, L-NAME, the guanylyl cyclase inhibitor, ODQ, and the protein kinase G inhibitor, KT5820. Abacavir also increased the cGMP level in rat basilar arteries. Abacavir-induced relaxation was also abolished by adenosine A2 receptor blockers. However, abacavir had no effect on ecto-5' nucleotidase and nucleoside transporters. Short-term and long-term treatment of abacavir did not affect acetylcholine-induced relaxation in rat basilar arteries.

Conclusion: Abacavir induces acute endothelium-dependent relaxation of rat basilar arteries, probably through the activation of adenosine A2 receptors in endothelial cells, which subsequently leads to the release of nitric oxide, resulting in activation of the cyclic guanosine monophosphate/protein kinase G-dependent pathway in vascular smooth muscle cells. It is speculated that abacavir-induced cardiovascular risk may not be related to endothelial dysfunction as abacavir does not impair relaxation of blood vessels. The most likely explanation of increased cardiovascular risk may be increased platelet aggregation as suggested by other studies.